Photoacoustic imaging is proposed as one of photo imaging technologies for irradiating a subject with light from a light source and imaging characteristic information in the subject which is obtained on the basis of the incident light. According to the photoacoustic imaging, the subject is irradiated with pulsed light generated from the light source, and an acoustic wave (typically, an ultrasonic wave) generated from a site where energy of the pulsed light propagated and diffused in the subject is absorbed is received. The characteristic information in the subject is then imaged by using the reception signal.
That is, according to the photoacoustic imaging, it is possible to obtain a distribution of the characteristic information (characteristic distribution) related to the light absorption at individual positions in the subject by utilizing a difference of absorption coefficients of light energy between a subject site such as a tumor and the other sites. The obtained characteristic distribution includes an initial sound pressure distribution, a light absorption coefficient distribution, a material concentration distribution, or the like.
According to NPL 1, a blood vessel is imaged by obtaining a total hemoglobin concentration distribution in the subject by a photoacoustic microscopy. With the photoacoustic microscopy according to NPL 1, light is sequentially focused on one point to another point (for each position) on a subject surface, and an acoustic wave generated from each position is sequentially obtained. The characteristic information based on the acoustic wave from the individual position is then arranged one by one. According to NPL 1, oxygen metabolism data such as a time course of oxygen saturation in blood obtained by using the photoacoustic microscopy is indicated, and a recognition that the above-described oxygen metabolism is useful as an index for a diagnosis is described.